Modern road pricing systems often rely on characteristics of a vehicle or its mode of use, e.g. the number of occupants of the vehicle, as in case of high-occupancy vehicle (HOV) lanes or express lanes which single-occupant vehicles may be allowed to use by paying a toll. This concept is also known as a “high-occupancy toll” (HOT) lane system. The amount of HOT may be inversely proportional to the number of occupants of a vehicle: the higher the number of occupants, the lower the toll. Other variable road pricing concepts can rely on vehicle characteristics or classes of characteristics, e.g. number of axles or wheels, trailer presence, or its environmental (air or noise) pollution class.
In most automatic free-flow toll charging systems electronic onboard-units (OBUs) are installed in each vehicle. These OBUs can communicate with roadside equipment belonging to the toll charger, such as DSRC (dedicated short range communication) or WAVE (wireless access for vehicle environments) beacons. By means of such DSRC or WAVE beacons vehicles can be localized and their road usage determined, calculated and charged.
To implement usage and/or vehicle dependent road pricing systems as discussed above, e.g. HOT lane systems, some basic toll charging parameters usually have to be set in the onboard-units, for example the number of current occupants of the vehicle, the vehicle class of the vehicle, etc., or registered in a database of the system. In such scenarios, controlling and enforcing the correct setting or registering of toll charging parameters becomes a critical point: If users with false parameter settings or registrations could not be detected, the effectiveness of the entire system would be undermined.
At present, one means of controlling and enforcing parameter settings or registrations is the personal observation of vehicles passing by, be it directly or via a camera link, and the comparison of the observation results with toll transactions generated by the vehicles passing by. This is a time consuming process and not feasible for a larger road network. It has therefore also been proposed to use electronic image processing means with which e.g. the number of occupants of a vehicle is automatically determined in a camera picture of the vehicle by sophisticated object recognition techniques. However, windshield glare and the shadowing of rear passengers by front passengers in a car deteriorate the recognition result significantly so that such systems are not reliable enough for employment in a commercial system on a large scale.